Enhancement of Impurity, Machinability and Mechanical Properties in Te-Treated 0Cr18Ni9 Steel

Abstract

To enhance the machinability and mechanical properties of 0Cr18Ni9 steel, free-machining element Te was introduced in this work. By adding various quantities of Te to steel, several machining and tensile tests were carried out. Results show that with Te addition of 530 ppm, the number of inclusion sizes below 1 μm disappeared. With raising Te from 360 to 530 ppm, more MnTe–MnS inclusions of 10–40 μm were in spherical shape; above 50 μm2, the ratio of inclusion area at 530 ppm was greatest among all, and the large-sized inclusions occupied a larger share. Te addition contributed to the surfaces of machining steels more smooth. The ultimate tensile strength of steel increased from 399 to 435 MPa. Te resulted in growth of sulfides and improved the machinability of steel. (a) The original sulfide in steel and its distribution is located along the grain bounday with sizes of 2–3 μm. (b) The Te-treated sulfide in steel and its distribution is still located along the grain bounday with most sizes exceeding 10 μm; and MnTe encapsulated the outer surfaces of MnS. (c) The Te-treated hot-rolling sulfide in steel, which is slightly elongated. The morphology of sulfide is changed from spherical shape to spindle shape. Both spherical and spindle shapes of MnS are beneficial to improving the cutting and mechanical properties of steel.